1. Field of the Invention
The present invention relates to a heat-sensitive recording material. More specifically, the present invention concerns a heat-sensitive recording material having a layer structure formed on a support, which includes a heat-sensitive recording layer containing at least two kinds of components that can develop colors by imagewise heating, a protective layer and the like. The recording material has good film quality, and is superior in transparency, gloss-applying property and light resistance, and has a high color-developing sensitivity, and can be written on using a thermal head or an infrared laser.
2. Description of the Related Art
In recent years, heat-sensitive recording techniques have developed greatly since recording devices therefor are simple, have high reliability and require no maintenance. As heat-sensitive recording materials, a variety of materials such as those materials which utilize a reaction between an electron-donating colorless dye and an electron-accepting compound and those materials which utilize a reaction between a diazonium salt compound and a coupler have been widely known.
Recently, studies have been vigorously carried out with respect to the heat-sensitive recording materials so as to improve characteristics thereof such as (i) coloring density and coloring sensitivity and (ii) fastness of coloring materials. However, the heat-sensitive recording materials have problems that when the materials having images are exposed to sunlight for a long time or when the materials are posted on a bulletin board for a long time in an office or the like, the background portions are colored by light, and image portions are discolored or faded. In order to improve coloring on the background portions, and discoloration and fading in image portions, various methods have been proposed. However, a method, which satisfies the above demands, overcome the problems and provide sufficient effect, has not obtained yet.
Need with respect to heat-sensitive recording systems in the various fields such as facsimiles, printers, labels and the like is increasing. Accompanying this is a large demand for a high writing sensitivity and a high image quality of obtained images in a heat-sensitive recording paper that is imagewise recordable by a heat-sensitive recording head or an infrared laser. Conventionally, in order for light resistance and high film quality of heat-sensitive recording material to be compatible with the high sensitivity of the same, one of two coloring components that react with each other by heating and form a color is enclosed in microcapsules. The microcapsules prevent the coloring components from reacting with each other and develop colors during storage of the heat-sensitive recording material. However, the microcapsules tend to aggregate with each other during a solution preparation process and while the prepared solution is preserved for an application process. Therefore, it has been difficult to provide uniform dispersion and to have uniform, high quality images. Moreover, in the case when the other coloring components for the coloring reaction are blended as an emulsion or when a latex dispersing solution is added to improve the film quality and the like, occurrence of the aggregation of microcapsules tends to be accelerated.
Further, hydrophobic compounds have been used by being dissolved in oil and the like then adding the oil to an application solution as an emulsion. However, in such a case, deposition of the hydrophobic compounds, combination of particles of the emulsion and the like tend to occur while the dissolution is preserved or while the dissolution is preserved in cold storage, and resulting in degradation in the image quality.
In order to improve durability, a layer containing capsules including a precursor of an ultraviolet-ray absorbing agent may be disposed at an outermost layer of a heat-sensitive recording material as a light-transmittance adjusting layer. However, in this case, these capsules tend to cause aggregation and the aggregation tends to cause failure in manufacturing processes. In this way, there is a demand for a heat-sensitive recording material which can provide superior image quality with uniform hues by preventing aggregations of microcapsules and latex, which are contained in layers of the heat-sensitive recording material, and achieving an uniformly dispersion thereof. However, in particular, there is a major problem, which is caused without regard to the layer structure of the protective layer, the heat-sensitive recording layer and the like. Namely, when a solid matter such as a latex or an emulsified dispersing substance coexists with microcapsules in a microcapsule dispersing solution, the possibility of aggregation occurring becomes extremely high.
An object of the present invention is to provide a heat-sensitive recording material which can improve the dispersing stability of coloring components and film-quality improving components contained in the heat-sensitive recording material, provide uniform image quality in obtained images, and form images having superior transparency and glossiness with high sensitivity, which images are formed by imagewise heating using a thermal head or an infrared laser. Another object of the invention is to provide a heat-sensitive recording material which can form images with uniform image quality and high sensitivity that are superior in transparency and glossiness, by preventing the aggregation of capsules enclosing coloring components, an emulsion substance and a latex comprised in a latex dispersing solution that is added so as to improve film quality (for example, improvement of a blister white-fogging defect that is generated by moisture or nitrogen gas that has been generated by photo decomposition of a diazo compound and expanded by heating at the time of printing).
In order to achieve the above-mentioned object, the inventors of the invention studied earnestly, and found that a polymer which has been known as an additive of photographic elements is very useful as a dispersant of microcapsules, an emulsion substance and a latex, thereby completing the present invention.
The first aspect of the invention provides a heat-sensitive recording material comprising a support having disposed thereon plural layers including at least one heat-sensitive recording layer and a protective layer, the heat-sensitive recording layer containing at least two components that react with each other to form color by imagewise heating,
wherein at least one of the plural layers contains a compound represented by the following general formula (I): 
wherein R represents one of a hydrophobic group and a hydrophobic polymer, and n represents an integer.
Examples of a layer which may be comprised in the plural layers include all layers which may be provided to and/or used for the heat sensitive recording material. For examples, back layer and the like are also included.
The second aspect of the invention provides a method of manufacturing a heat-sensitive recording material, which includes a support and plural layers including a protective layer and at least one heat-sensitive recording layer containing at least two components that react with each other to form color by imagewise heating, the method comprising the steps of:
preparing a coating solution containing the at least two components that react to form a color by imagewise heating and a compound represented by the following general formula (I); 
applying the solution onto a support and drying the solution to form the heat sensitive recording layer; and
forming the protective layer,
wherein, in the general formula (I), R represents one of a hydrophobic group and a hydrophobic polymer, and n represents an integer.